What is Dutch Elm Disease?

Brief History

Dutch elm disease (DED) is a devastating fungal disease that affects elm trees (genus Ulmus). It was first identified in the Netherlands around 1910, with the name "Dutch" referring to the Dutch scientists who initially studied it. The disease spread rapidly across Europe and reached North America by the 1920s, likely through infected timber imports. By the mid-20th century, DED had decimated millions of elm trees, particularly American elms (Ulmus americana), which were once dominant in urban and natural landscapes. A second, more virulent strain emerged in the 1960s, further worsening the epidemic. Today, DED remains a significant threat to elm populations worldwide.  Minnesota's first case of Dutch elm disease was detected in St. Paul in 1961 and has been reported in all but a few of Minnesota's 87 counties.

Science

DED is caused by two species of fungi: Ophiostoma ulmi (responsible for the initial epidemic) and the more aggressive Ophiostoma novo-ulmi. These fungi invade the tree’s vascular system, blocking water and nutrient transport, leading to wilting and death. The fungi are primarily spread by Elm bark beetles (Scolytus spp. and Hylurgopinus rufipes): These beetles carry fungal spores while feeding or breeding in elm trees.

Identifying Characteristics

Symptoms of DED typically appear on the elm tree in spring or summer and include:

• Wilting leaves: Leaves on one or more branches turn yellow, curl, or brown prematurely, often starting at the tree’s crown.
• Flagging: Affected branches display drooping, wilted leaves, resembling a flag.
• Dark streaks: Brown or black discoloration in the sapwood under the bark, visible when a branch is peeled or cut.
• Dieback: Progressive death of branches, often leading to the entire tree’s decline within weeks or months.
• Beetle activity: Small exit holes or sawdust-like frass on the bark indicate elm bark beetle infestation.

Spread of Dutch Elm Disease 

Elm Bark Beetles 

The Dutch elm disease fungus is spread primarily by the European and the native elm bark beetles, both of which are about 1/8 inch long (3 mm).  The European elm bark beetle (Scolytus multistriatus) is the primary vector (disease carrier) in the southern portion of Minnesota, including the Twin Cities Metropolitan area, while the native elm bark beetle (Hylurgopinus rufipes) is the primary vector in the northern region of the state.

Adult elm bark beetles lay their eggs under the bark of recently dead or dying elm trees in brood galleries (tunnels in the inner bark where the eggs are laid) constructed by the female beetles.  Eggs laid along the brood galleries hatch and the larvae feed, producing their own galleries at right angles to the original egg laying galleries.

If the breeding takes place in diseased wood, the Dutch elm disease fungus spores grow in the beetle brood galleries.  These sticky spores adhere to the bodies of the adult beetles before they emerge from the tree.  The beetles then fly to a live elm tree and bore into small 2-4 year old branch crotches in the upper canopy to feed.  The germinating fungus spores enter the water conducting vessels through the beetle feeding wounds.  Another elm tree is then infected with the disease.  After feeding, the female adult beetles will seek out recently dead or dying elm wood in order to breed and lay eggs, producing yet another generation of beetles and repeating the cycle.  There are generally 2-3 generations of bark beetles per year.  Once an elm tree is infected, the disease can spread underground to nearby healthy elms through grafted root systems.

Dutch Elm Disease Management

• Sanitation: Promptly remove and destroy infected trees or branches to reduce fungal spread. Dispose of wood by burning, chipping, or burying (if permitted locally).
• Beetle control: Apply insecticides to healthy elms to deter bark beetles. Timing is critical, targeting beetle activity periods (spring/early summer).
• Root graft disruption: Sever root connections between adjacent elms using trenching or chemical barriers to prevent fungal transmission.
• Fungicide injections: Inject systemic fungicides (e.g., propiconazole) into healthy or mildly infected trees to protect against infection. This is expensive and requires professional application every 1–3 years.
• Monitoring: Regularly inspect elms for symptoms, especially in urban areas or near known infections.

Licensed Tree Contractors & Other Resources

Looking for a reputable tree care company to remove diseased elm trees? View the list of licensed tree contractors.

University of Minnesota Extension Dutch elm disease

Minnesota Department of Agriculture Dutch elm disease